Manufacture of fibrids of polyolefins

Abstract

Fibrids of polyolefins showing a high degree of fibrillation and a high specific surface area are obtained by flashing a pressurized solution of polyolefin in pentane or in a pentane-containing solvent mixture at a temperature above the boiling point of the solvent by passing said solution through an orifice into a space which is at a lower pressure and in which shearing forces are applied to said solution. The fibrids directly obtained may be used, for example, for the manufacture of paper or for the manufacture of textile-like webs.

We claim: 
     
       1. A process for the manufacture of discrete fibrids of polyethylene having lengths of 1 to 50 mm and thicknesses between 2 and 30 μm which comprises (a) dissolving in a pressure vessel polyethylene, obtained by low-pressure polymerization of ethylene, in a solvent which is a mixture of pentanes and a naphtha cut boiling at 25° to 140° C. and containing pentanes in an amount of from 5 to 50% by weight, said pentanes being selected from the group consisting of n-pentane, isopentane, cyclopentane and neopentane,   (b) maintaining the vapor pressure in said pressure vessel at 4 to 60 atmospheres and maintaining the temperature of the polyolefin solution in said pressure vessel at temperature of 80°  250° C and above the boiling point of said solvent at standard pressure,   (c) passing said polyethylene solution from said pressure vessel through an orifice into a space maintained at lower temperature and pressure than those in said pressure vessel,   (d) flashing off said solvent in said space from the solution passed through said orifice to produce a tangled mass of said fibrids, said amount of said pentanes in said solvent further being sufficient to cause the polyethylene to separate in form of discrete fibrids upon the flashing off of said solvent in said space, and   (e) drying the resultant polyethylene fibrids.   
     
     
       2. A process as claimed in claim 1, and the further step of disentangling the dried fibrids by combing, brushing or picking to obtain a free flowing and transportable mass of said polyethylene fibrids having said lengths and said thicknesses. 
     
     
       3. A process as claimed in claim 1, wherein said polyethylene has a density in the range of 0.915 to 0.965 g/cm 3 . 
     
     
       4. A process as claimed in claim 1, wherein said polyethylene has a melt index (as determined by ASTM D 1238-65 T at 190° C and a load of 2.16 kg) in the range of 100 g/10 minutes to 0.01 g/10 minutes.